I saw that a Yamaha keyboard i would like to buy has a spec called 'arpeggiator'. what is an arpeggiator? what can i do with it? i looked around the web but can't find an explanation anywhere.

An arpeggiator allows you to hold down a chord, and plays the notes of the chord individually. For instance, if you played a CMajor (C-E-G), the arpeggiator would play C-E-G-E-C... over and over again. A good arpegiator will have many different patterns that it can play, suited for different kinds of music. You can also adjust the speed. A good example of using an arpeggiator would be a walking bass line, where all you have to do is hold down the notes you want and it plays the notes for you. Or like Jamaican steel drums (or whatever the hell they're called) or a zylophone pad. Manually playing all those trills could give you quite a workout!

An arpeggiator is a device that automatically steps one note at a time through a group of notes that are held down or latched together . Some will go up or down or up and down through the notes that you hold down . Some you can specify the order in some random ways . It can be very useful in dance music , it's almost like having an analogue sequencer in that while the notes are playing - you can open and close the filter for a very electronic feel . That is if your synth is cool enough to have real time controls .